1. Field of the Invention
The invention relates to an optical fiber connector and the use of radiation in the visible portion of the spectrum to cure a photocurable adhesive in an optical fiber connector to bond the optical fiber, the reinforcing fibers and the optical holder into a unified structure, in order to provide an improved connection between two optical fibers or an optical fiber and an optoelectronic component.
2. Description of the Art
Optical fibers have replaced copper wire as the preferred medium for carrying telecommunications signals. As with copper wire, it is necessary to provide for the interconnection of optical fibers during installation, repair or replacement of the fibers, and to terminate the fibers onto active optical devices. There are generally two kinds of interconnection devices, splices and connectors. The term "splice" usually refers to a device, which provides a permanent connection between a pair of optical fibers. The term "connector," in contrast, usually refers to a device, which may be engaged and disengaged repeatedly, often with a different plug or receptacle. A connector may also refer to the plug portion of a fiber termination, which is attached to an optical device. Optical devices include, for example, optical sensors (photoelectric diodes) and light sources (LED's, laser diodes). The termination of an optical fiber may be indirect, i.e., the fiber may be connected to some other (passive) optical device such as a beam splitter or polarizer, before the light beam is directed to the active optical device. The present invention is generally directed to a connector, although this term should not be construed in a limiting sense since the present invention may inherently provide a permanent, as well as temporary connection or termination.
In the fiber optic connector described in U.S. Pat. No. 5,381,498, the connector has a plug and a receptacle, the plug having a fiber-receiving, V-shaped groove for each fiber to be interconnected, with the end of the fiber terminating in the middle of the groove. The receptacle has a plate which retracts as the plug is inserted, whereby another fiber is lowered into the V-groove of the plug. Upon full insertion of the plug, the two fiber ends are in contact, and the fiber secured to the receptacle is elastically deformed to maintain a continuous compressive load between the terminal ends of the fibers. The connector provides for the quick disconnection and reconnection of a plurality of optical fiber pairs, without the use of ferrules or other alignment members. High strength fiber may be used to withstand repeated insertions and bowing of the fibers. The exact lengths of fibers (i.e., the relative locations of their terminal ends in the plug and receptacle) are not critical since tolerance is provided by the slack taken up in the bowed receptacle fiber (the terminal portion of the fiber secured to the plug does not bow, but always remains straight). The ends of the fibers may be prepared by simply cleaving and beveling; the end faces may optionally be cleaved at an angle (i.e., non-orthogonal to the fiber axis) to reduce signal reflections.
Many fiber optic splices employ plate elements having fiber-receiving grooves, with mechanisms for clamping the terminal ends of the fibers in a common groove. Some of these devices are designed to interconnect a plurality of pairs of fibers, such as the splice shown in U.S. Pat. No. 5,151,964. In U.S. Pat. No. 4,028,162, fibers approach alignment grooves at a glancing angle and are held temporarily while a connector plate is adhered to the interconnected fibers. For other examples of techniques involving bowed fibers entering alignment grooves, see U.S. Pat. Nos. 4,077,702, 4,148,559, 4,322,127 and 5,080,461, and French Pat. Application No. 2,660,442. Some of the connector designs using the principle of bowing a fiber into a fiber-alignment groove are rather complex and require many parts, such as the designs seen in U.S. Pat. Nos. 4,045,121, 4,218,113 and 4,767,180.
In order to provide a termination or interconnection with the required strength without damaging the system, the fibers must be secured to the connector body to inhibit or at least reduce the relative movement between the optical fiber and its outer sleeve.
Such an attachment system may be mechanical, such as a clamp or set of clamps or it may be a type of adhesive. A mechanical system may also include strength members such as layers of stranded steel wire, as disclosed in U.S. Pat. No. 5,539,849.
Useful adhesives for termination must be capable of bonding to the outer surface of the fiber, which may be formed from materials such as glass, epoxy silicones, and the like. It also must be capable of bonding to other materials used in fiber optic cables and their terminations, such as polymeric coating layers, and strengthening fibers used to surround the optical fibers, and plastics from which the holder is formed. The strengthening fibers are typically aromatic polyamide fibers derived from p-phenylenediamine and terephthaloyl chloride, available commercially as Nomex.RTM. or Kevlar.RTM..
U.S. Pat. No. 4,699,462 discloses a method for forming a termination between a fiber optic cable having a centrally positioned optical fiber, a plurality of surrounding reinforcements, and a component housing. An adhesive, preferably a heat activated adhesive, is applied within the termination and heat shrink tubing is applied in order to force the reinforcement fibers into adhesive engagement with the adhesive layer. Bond formation occurs primarily at the interface between the cladding on the optical fiber core, and reinforcement strands. The adhesive does not provide bonding to the heat shrink tubing; it is present to provide reinforcement to the termination.
U.S. Pat. No. 5,058,984 discloses a fiber optic cable connector comprising a plastic outer sleeve to be optically coupled to another optical fiber cable, carrying at one end, connection means for coupling, a tubular gripping member which adheres the fiber to the outer sleeve or holder, which is deformed by application of force so as to grip the end portion of the plastic outer sleeve and a ferrule mounted within the other end of the connector body supporting an exposed end portion of an optical fiber. The optical fiber is adhered to the ferrule with adhesive material. The ferrule is ceramic and the exposed end of the fiber is set with a light curable resin, generally blue light where the ferrule is formed of zirconia. This allows a setting time to be reduced to about 60 seconds. It is specifically disclosed that an irradiation curable adhesive might not adhere sufficiently strongly to the plastics outer sleeve; therefore the adhesive material is used to secure the end portion within the ferrule, and does not need to provide any adhesive to the plastic outer sleeve.
As can be seen, even with the use of adhesives, conventional fiber optic connector assemblies have required the use of additional positioning or bonding means in order to resist disruptive force. It would be very desirable to eliminate such means and be able to provide a unified system wherein the bond is formed solely from an adhesive which adheres the optical fiber to the outer holder of the connector, and adheres to the fiber as well as the coating and strengthening fibers without requiring additional positioning means such as heat shrink tubing, gripping members and the like.
U.S. Pat. No. 5,525,648 discloses a treatment method for application to dentin and cervical enamel or adhering to hard tissue in a high humidity environment. Primer compositions disclosed bond strongly to dentin, and exhibit high shear strength, and include an acid and a film former, which are applied and then hardened. A wide variety of acids are useful, including organic, inorganic, solid and liquid acids. Useful film formers are water dispersible and may be selected from many polymers, monomers and mixtures. After standing time to achieve priming, the primer, optionally, with an additional layer of film former is then hardened by use of a polymerization catalyst.
U.S. Pat. No. 5,545,676 discloses a three component or ternary photoinitiator system for use in additional polymerization. A variety of acrylate monomers are disclosed. The system is disclosed to provide a combination of cure speed, cure depth and shelf life, and is disclosed to be useful in color profiling systems, curable inks, printing plates, photoresists, coated abrasives, photocurable adhesives and composites, e.g., for dentistry or autobody repair.
The present invention provides a fiber optic connector using a visible light photocurable adhesive composition to bond the optical fiber(s), the strengthening fibers surrounding the fiber and a coating layer thereover into a unified structure. The system provides a fast cure, good depth of cure, and a safe, low energy means for providing the bond, which can be easily accomplished by a tradesperson.